OF CENTRAL FORCES. 



33 



The whirling-table is a machine contrived for shew- LECT. 



ing experiments of this nature. A A is a strong frame 



H. 



The whirl- 

 ing-table 

 described. 



of wood, B a winch or handle fixed on the axis C of 

 the wheel D, round which is the catgut string F, which 

 also goes round the small wheels G and K, crossing 

 between them and the great wheel D. On the upper 

 end of the axis of the wheel G, above the frame, is fixed 

 the round board d, to which the bearer M S X may be 

 fastened occasionally, and removed when it is not 

 wanted. On the axis of the wheel H is fixed the bearer 

 NTZ; and it is easy to see that when the winch JB is 

 turned, the wheels and bearers are put into a whirling 

 motion. 



Each bearer has two wires, W, X, and Y, Z, fixed 

 and screwed tight into them at the ends by nuts on the 

 outside. And when these nuts are unscrewed, the wires 

 may be drawn out in order to change the balls U and V, 

 which slide upon the wires by means of brass loops, 

 fixed into the balls, which keep the balls up from touch- 

 ing the wood below them. A strong silk line goes 

 through each ball, and is fixed to it at any length from 

 the center of the bearer to its end, as occasion requires, 

 by a nut-screw at the top of the ball ; the shank of the 

 screw goes into the center of the ball, and presses the 

 line against the under side of the hole that it goes 

 through. The line goes from the ball, and under a 

 small pulley fixed in the middle of the bearer ; then up 

 through a socket in the round plate (see S and T) in 



D 



